With the term “hopper” in the present description and in the claims, it is meant any type of tubular container, both open and closed at the top (in this case, also known as “silo”), having a variously configured constant cross-section, e.g. circular, square, or rectangular, terminating with a tapered lower section equipped with a suitable discharge mouth, generally controlled by a suitable discharge valve. A hopper, as is known, is meant to be normally loaded with granular material at an upper section thereof; possibly, after having undergone a type of treatment, such as heat or aeration treatment, the material is then discharged through the discharge mouth. As is known, in recycling or transforming many granular plastic materials into manufactured articles, one of the most important treatments consists of the crystallization process, to which the granular polymer material must be subjected.
The granular material to be treated has semi-crystalline structure, i.e. characterized by crystalline zones with macromolecules arranged in an ordered manner with respect to the others, forming a so-called “long-range order”, and by amorphous zones comprising macromolecules arranged in a disordered manner and thus lacking long-range order.
Generally, it is possible to obtain the crystallization of a polymer when the following conditions are met. First, the polymer must have its own polymer chains at least partly ordered according to specific composition and configuration parameters: i.e. it must be equipped with sufficiently long, ordered chain segments. Furthermore, the crystallization process must be feasible both from a thermodynamic and kinematic standpoint. In other words, a sufficiently long time must be provided for the rearranging of the disordered structure of the polymer chains, such a rearranging occurring by translation of its chain lengths until they have an ordered configuration in space.
In order to induce crystallization of amorphous polymer material, it is necessary to provide energy to the material in the form of heat, using a crystallizer apparatus comprising a top-closed hopper or silo. In practice, the amorphous polymer material in granule form is first loaded at the upper part of the hopper through a loading mouth, and then heated by means of hot air insufflation at a lower zone of the hopper to a temperature greater than the glass translation temperature T9, but less than its melting temperature Tm.
The glass transition temperature T9 is defined as the temperature beyond which the amorphous polymers gradually pass from a solid state to a so-called “rubbery” state, in which the spatial arrangement of the polymer chain segments (comprising 30-50 atoms, according to the most reliable studies) can vary.
Advantageously, the hopper of a crystallizer is equipped with a mounted for rotation and extending along the longitudinal axis of the hopper for much of its length, on which horizontal blades are fit or fixed. Such blades are suitably spaced from each other in a vertical sense, thereby acting as stirring blades for the granular material being treated. For such purpose, at the top of the hopper or silo, a gearmotor group is provided for, intended to actuate the rotatable shaft and thus the blades. The stirring action of the blades maintains the crystal “suspension” that forms during the crystallization process in a homogeneous suspension, so as to avoid the formation of agglomerates, with consequent formation of undesired lumps in the granular material.
After the specific time for treating the granular material has passed, the crystallization process is completed and the granular polymer material in the hopper thus has an ordered structure. The material can then be cooled before it is discharged through the discharge valve.
During the granular polymer crystallization process, it may occur that, by mistake, the granular material loaded in the hopper is brought to an overly high temperature, causing its melting. The melted material must be immediately removed from the hopper or silo before it solidifies. It is thus quite necessary for an operator to have a quick and easy access inside the hopper, through which he can easily carry out cleaning and material removal operations.
At the state of the art, small-capacity hoppers have already been proposed (with max 50-100 It. capacity), closed at the top and comprising a lower tapered section, equipped with discharge mouth controlled by a suitable valve, supported by a support framework and hinged to an upper tubular section, such that the latter can be angularly displaceable by the operator's hand between a work position, in which it is found mating on the vertical of the lower section, and an open position, in which it is angularly removed (overturned) from the lower section, thereby allowing an easy access. The upper tubular section results manually overturnable with respect to the lower tapered section and, if necessary, an operator could thus easily access the hopper interior for maintenance and cleaning operations.
Nevertheless, this type of hopper cannot be employed for containing and/or treating large quantities of material (>100 It) since the size and weight of the upper section of the hopper would not allow the operator to manually open and close the hopper itself. Furthermore, in the case, for example, of crystallizer hoppers or dehumidification hoppers, the overturning of the upper section of the hopper with respect to the lower tapered section would be impossible or in any case severely hampered by the presence of permanent connections to feed ducts of granular material, hot air, etc. which would have to be previously disconnected from the hopper before its opening. This would lead, furthermore, to long operation dead times for the trained personnel.
Document DE-90 11 556 discloses a silo for loose material having an upper tubular section connected to a lower section provided with a discharging mouth. The lower section comprises an upper portion of substantially hemispherical configuration connected to the upper section of the silo, and delimiting a substantially oval opening, and a lower tapered portion, in which the discharging mouth is formed, and which is hinged to said upper hemispherical portion through suitable hinging means. With such a configuration, the lower tapered portion of the lower section of the silo can be angularly displaced from a closure position, in which it closes the oval opening of the substantially hemispherical upper portion, and an open position in which it is displaced from the oval opening to give access to the inside of the silo.
Document DE-94 16 198 teaches connected means designed to connect the discharging mouth of a silo to ducts and pipelines having cross section different from that of the discharging mouth. The connecting means are hinged to the lower tapered portion of the silo.
The silos described in the above identified documents do not provide an easy access to the inside thereof.